Even though the amount of waste that is recycled is gradually increasing, huge amounts of waste are still tipped into landfill sites each year. Once you have recycled as much waste as possible, there are generally no other practical options at present.
Waste contains a wide range of types of contaminants that are harmful to our environment. For example, it is not often realized that the waste contains substantial amounts of toxic metals, often from packaging materials. Rainfall runs through the landfill sites and gradually dissolves the huge range of contaminants so that, as the rain water runs off the site, it is highly contaminated and cannot be safely discharged to the environment.
Treatment is therefore required. The question is: What are the actual goals for treatment and what type of treatment is best suited to achieve those goals?
The goals depend to some extent on the location of the site, simply because other factors such as availability of water can be important considerations. The following list includes the most common requirements.
- Treatment of leachate so that, after treatment, it can be safely discharged to the environment.
- A system design that acknowledges that the quality of the untreated leachate does vary. For example, there will be a far higher volume but probably a lower concentration of the contaminants when there is a period of higher rainfall. On the other hand, if there has been little or no rainfall for a long time, and then it starts to rain hard, the leachate may well have both a high flow and a high concentration.
- What is to be done with the treated leachate? Is it simply discharged to foul sewer or a local river? In areas of severe water shortage, perhaps it needs to be directly re-used?
- What are the system operating costs? Basically the entire treatment system just increases the overall operating costs for each landfill site. The only reason for having it is to protect the environment. Therefore operating costs should be as low as possible.
- Can the chosen plant be easily and quickly expanded at reasonable cost? Clearly, as each landfill site expands with time and / or the average rainfall increases, often a larger treatment plant is required a little later on.
Basic Types of Leachate Treatment
A number of basic types of treatment are available:
- Conventional Biological Treatment systems (MBR/ MBBR/ SBR/ UASB/ RBC etc.) have been used on many sites. However, they do not remove metallic contaminants, and cannot be easily and cheaply expanded at a later date.
- Engineered Wetlands need a great deal of space and, although relatively cheap to operate, cannot be expanded when necessary without a great deal of effort, land and cost.
- Tankering is not practical or cost effective in any but the smallest applications.
- Membrane systems, including Reverse Osmosis (RO), Microfiltration (MF), Ultrafiltration (UF) and Nanofiltration (NF) are now the predominant type of technology used.
Of these, RO produces the lowest percentage of final wastewater for disposal and the highest quality treated water, which then be either safely disposed to a water course or, if required, directly re-used.
As mentioned before, membrane-based systems are particularly well suited for separation of contaminants in water. However, in particularly challenging applications, such as leachate from landfill sites, plate and frame module technology has really big advantages over other designs.
For such challenging applications, Circular Disk Membranes have proved themselves to be very well suited. This is in part because they can handle a much higher SDI (Silt Density Index) than other membrane systems. SDI is a measure of the amount of suspended solids present in the leachate and, for many other system types, blockage caused by these solids is a major issue!
Advantages of CD Membrane Systems
- Low energy costs
- High water recovery rates
- Long membrane Life
- Very low chemical consumption for the process
- Small footprint
- Proven and reliable technology
- RO proven technology able to meet discharge consents
- Modular design can be adapted for changes in UK legislation throughout the life of the plant
- No leachate tanker movements from site
- Quick to install and expand when required
- Standard, modular design can be rolled out across all client sites.